1. Field of the Invention
The present invention relates generally to optical fibers, and more specifically to fibers suitable for transmitting UV light.
2. Technical Background
Optical fiber has become a favorite medium for telecommunications due to its high transmission capacity and immunity to electrical noise. Specialized fibers for UV applications have been developed. However, there has not much work done in the area of the composition of silica glass in the fiber other than using either cores consisting of Ge doped silica, or, more typically, fibers with pure silica core fibers with a Fluorine-doped cladding.
Multi-mode (MM) optical Fibers for UV spectral range that comprise pure silica glass core can not supply high (broad enough) bandwidth due to requirement for fiber core graded index profile, graded index is much more difficult to make than with a step index profile with a pure silica core.
While Single Mode (SM) fibers can be made using a step index pure silica core, they typically utilize cladding down-doped to provide the required core delta (relative to cladding). However, when such fibers are heated in order to make optical fiber components such fused biconic taper couplers, for example, fluorine diffuses and migrates into the fiber core, compromising the coupler's performance, or making its loss too high. Optical fiber components can benefit from having a less thermally diffusive index modifying dopant than what is used make pure silica core fibers. Optical fibers with Ge doped cores can utilize pure silica claddings, or silica cladding with less F then what is required by the fibers with pure silica cores. However, MM and SM optical fibers with Ge doped core suffer from relatively high optical loss (e.g., >0.15 dB/m at λ=400 nm and greater than 0.08 dB at λ=425 nm), due to the presence of GeO2 in the core.